1. Field of the Invention
The present invention generally relates to microwave motion and Dual-Tech (Microwave/PIR) motion sensors, and more particularly, a method and apparatus using microwave motion sensors having a reflector for enhanced lookdown ability.
2. Description of the Related Art
Security systems and automated manufacturing systems, as well as, other automated processes are employing microwave (MW) motion sensors for motion detection. MW motion sensors typically include a microwave transceiver as an active device employing electromagnetic waves lower in frequency than visible light. MW motion sensors transmit a microwave signal toward a region to be monitored and in the event that movement is detected within the region, the microwave signal is reflected back (echo) from the movement and is modulated due to the Doppler Effect. When a signal is reflected from a moving object (target) it is shifted in frequency. This shift in frequency is called the Doppler Effect and is directly proportional to the targets velocity relative to the sensor. A maximum frequency shift is when the target is moving straight at the sensor, and a minimum frequency shift is observed if the target is moving at a 90 degree angle towards the target.
In certain security and other automated applications or systems, a MW sensor may be mounted on a wall to monitor a room or part of a room. In this situation a microwave reflector is employed to enhance the coverage of the MW motion sensor.
Known MW motion sensors may include an antenna having a plurality of microstrip radiating elements (antenna patches) and a strip of copper foil 130 disposed in front of the antenna aperture so as to reflect an upper portion of the emitted radiation from the plurality of microstrip radiating elements. An antenna aperture is the portion of a plane surface very near the antenna and normal to the direction of maximum radiant intensity through which the major part of the radiation passes. Thus, a reflector or strip of copper foil provides enhanced microwave amplitude at low incident angles, thereby effectively reducing a blind zone beneath the microwave transmitters by reflecting part of the main beam. Such MW motions sensors are described in Applicant's co-owned copending application U.S. Ser. No. 11/940,038 which is herein incorporated by reference in its entirety.
A drawback of current MW motion sensors is that they enhance detection underneath the sensor by reflecting part of the main beam. Thus, the loss of strength of the main beam may be detrimental to detection in the protected region by the antenna. Further, current MW motion sensors and systems do not provide for detection of tampering, e.g., masking to the MW/Dual Tech sensors, to disable the sensors when the security system is in unarmed/disarmed mode. Masking may include damaging or covering the MW or Dual Tech motion sensors when the security system is not armed to disable the sensor for later use when it is armed.
Therefore, a need exists for a system or method to detect tampering of a MW or Dual Tech motion sensor to ensure the operability of the sensor when armed or in alarm mode.